A turbocharged air induction system includes a turbocharger that compresses air flowing into the engine, thereby forcing more air into an associated combustion chamber. The increased supply of air allows for increased fueling, which may result in increased power. A turbocharged engine typically produces more power than the same engine without turbocharging.
An exemplary turbocharger is described in U.S. Patent Publication No. 2011/0252790 to Lotterman et al. that published on Oct. 20, 2011. The '790 publication describes a turbocharger having an axial turbine with a spiraling volute passageway. The axial turbine receives a circumferential exhaust gas stream that drives a turbine wheel around an axis of rotation. The spiraling passageway accelerates the speed of the gas stream to supersonic speeds. The exhaust gas stream may have both an axial component and a circumferential component, and is ultimately released from the turbine in an axial direction.
Although the turbocharger of Lotterman et al, may provide accelerated airflow through the turbine, it may still be less than optimal. In particular, the turbocharger of Lotterman et al. directs a non-uniform and poorly guided axial flow through the turbine wheel for wide operating conditions. This poorly guided non-uniform flow may create high energy losses, reduced aerodynamic efficiencies, and increased mechanical or vibrational stresses (or strains) on the turbine during operation due to flow misalignment (high incidence) with the blades of the turbine at wide operating conditions. Also, the axial turbine stage shown in Lotterman et al. is a high reaction stage, which may lead to supersonic flows with higher aerodynamic losses (passage and secondary flows) in blade passages, as compared to low reaction stages at similar turbine stage loading conditions.
The disclosed turbocharger is directed to overcoming one or more of the problems set forth above and/or other problems of the prior art.